Fusible fire sensing tape formed of metal particles dispersed in a flexible plastic binder



Jan. 10, 1967 H. c. PELTIER 3,297,846

FUSIBLE FIRE SENSING TAPE FORMED OF METAL PARTICLES DISPERSED IN AFLEXIBLE PLASTIC BINDER Filed Sept. 22, 1964 FIG.

1 2x //2 24 m D) J INVENTOR. HEN/FY c. PEA 7/5,? 42 F /G. 3 42 BY3,297,846 FUSlliiLE FIRE SENSENG TAPE FORMED F METAL PARTICLES DISPERSEDIN A FLEX- IELE PLASTIC BINDER Henry C. leltier, 256 Harrison Ave, Lodi,NJ. 07644 Filed Sept. 22, 1964, Ser. No. 398,366 8 Claims. (Cl. 200-142)This invention relates to fire sensing tape for use in a fire detectionand extinguishing system and to a system incorporating such a tape.

It is an object of this invention to provide a fire sensing tape inconjunction with a fire detection and extinguishing system which reactsto flame or elevated temperatures at great speed, so as to enable theextinguishing system to discharge a fire extinguishing agent and bringthe fire under immediate control before the fire has gained anappreciable headway.

It is known in the art to provide a fire extinguishing system which isactuated upon the fusion of a low-temperature melting element ortrigger. An overhead fire sprinkler system is a typical example of sucha system.

Said fusible element commonly holds closed a valve on the discharge portof a sprinkler nozzle, which prevents the egress of a fire-extinguishingmedium under pressure. When a fire occurs, the fusible elementeventually is heated to its fusion temperature and melts, clearing theport and permitting the sprinkler to discharge.

The above-described sprinkler system has a defect characteristic of anyfire sensing system which depends for actuation upon the fusion of alow-temperature melting metal. This defect is that the system does nothave the sensitivity and fast reaction time required in many criticalapplications. Even a short exposure to intensive flame will destroy alarge quantity of information-storage cards or delicate electricalcomponents. Further, as the fire increases in intensity toward itsmaximum burning rate, it becomes exceedingly more diificult to quench atthe first burst of the fire extinguishing medium, and a prolonged periodof discharge soon becomes necessary to put out the fire.

One reason for the insensitivity of the mentioned type of system is thefact that the fusible element typically has a substantial heat storagemass and is engaged as Well by a holder of considerable heat storagemass. These masses act as heat sinks which slow the tempera ture rise tothe trigger temperature. Before the trigger element reaches its meltingpoint, the mass immediately adjacent the heat-sensitive element must beheated to substantially the same temperature.

Another factor also prevents any system employing a fusible element fromworking at a fast reaction rate. This is a physical characteristic ofsuch materials that has been mentioned above in passing, to wit: thatthe fusion temperature must be maintained for a certain period of timeuntil a sufiicient quantity of heat has been imparted to the material tocause it to change from the solid to the liquid phase. The absorption ofthis quantity of heat necessarily requires a delay in the completefusion of the fire alarm trigger, with a resultant delay in theactuation of the system.

It is the primary object of my invention to provide a fire sensing tapefor use in a fire alarm system which reacts to flame and hightemperature at a rapid speed and without the delay inherentinfusible-element systems.

It is a further object of my invention to provide a fire sensing tape ofthe character described which upon its degradation or destruction byfiame or high temperature causes a fire extinguisher to discharge so asto bring the conflagration under immediate control.

It is yet another object of my invention to provide a fire sensing tapeof the character described which is an United States Patent 0 3,297,846Patented Jan. 10, I96? elongated flexible element and which can bereadily fixed in a continuous length to walls, ceilings or any surfaceareas of varied structures whereby the tape can be brought in closeadjacency to any potential source of fire.

It is a further object of this invention to provide a fire sensing tapeof the character described in conjunction with a fire detection andextinguishing system wherein the extinguishing medium is dischargedthrough perforated ducts whereby the extinguishing medium is directed tospecified sites in a structure remote from the source of the medium.

It is another object of my invention to provide a fire sensing tape ofthe character described wherein the tape has the characteristic ofaccelerating its own destruction upon the application of flame or heat.

It is a further object of my invention to provide a fire sensing tape ofthe character described wherein the continuous length of the tape canreact to different temperatures at different positions along its lengthso that when a structuremaintains different areas at differenttemperature levels, the tape will actuate its fire extinguisher systemat an approximately constant increment above normal temperature.

These and various other objects and advantages of my invention willbecome apparent to the reader in the following description.

My invention accordingly consists in the features of construction,combinations of elements, arrangements of parts and series of stepswhich will be exemplified in the fire sensing tape and systemhereinafter described and of which the scope of application will beindicated in the appended claims.

In the accompanying drawings in which is shown various possibleembodiments of my invention,

FIG. 1 is a schematic view of my fire sensing tape incorporated into afire detection and'extinguishing system;

FIG. 2 is an enlarged fragmentary perspective view of the fire sensingtape; and I FIG. 3 is a top plan view of my fire sensing tape the formof. a mat.

Referring now to the drawings, and especially FIG. 2, the referencenumeral 10 denotes a fire sensing tape constructed in accordance withthe teaching of my invention. The fire sensing tape comprises anelongated electrically non-conductive flexible carrier 12 of syntheticplastic sheet material and an elongated flexible electrically conductivestripe 14 fixed to an exposed face 16 of the carrier. In a preferredform of my invention, a pressuresensitive adhesive layer 18 is fixed tothe opposed (back) face of the carrier 12 and is utilized to sticklengths of tape 10 to any solid area of a structure to be protectedagainst the outbreak of fire.

' The stripe 14 is, as has been mentioned, electrically conductive andflexible and is narrowerer than the carrier 12. In the illustratedembodiment of my invention, the stripe 14 overlays only a small fractionof the exposed (front) face 16 of the carrier, and is disposedintermediate, and preferably centered between, the side edges, of thecarrier.

It may be advantageous to note at this point thatthe term exposed facerefers to that face of the tape which, when the tape 10 is attached to,say, the walls or ceiling of a room, is most directly subject to theeffect of flame or' heat. In other words,- it is the face which is notdirectly adhered to the protected structure.

The stripe 14 is continuous along the length of the carrier and, as willbe subsequently detailed, forms the major portion of an electrical loopwhich is part of the fire detection and extinguishing circuit. Thestripe is composed of finely divided particles of a low resistivity,high melting point metal or metal alloy held in a binder,

the metal preferably being silver. The term low resistivityrefers to theresistance of conductors typically used in electrical circuits which arein the vicinity of 2 microhm-cm. The conductor should transmitelectrical energy with a minimum of PR loss, so as not to affect thetemperature sensitivity of the tape itself.

The term high melting point refers to the melting point of a metal whichfuses at a temperature far above the temperature at which a normallysensitive fire extinguisher system should be set off to be effective inprotection. For this purpose, a high melting point would be consideredin the range startingabout at 700 F. The melting point of the metal inthe stripe is thus far higher than the melting temperature of fusibleelements such as Woods metal or lead alloys used in fusible trigger fireextinguishing systems.

The binder for the metallic particles must be flexible so thatthe stripe14 is flexible on the carrier 12, and serves to hold the metal particlesin contiguous adjacency to render the stripe conductive as well as ameans to adhere the stripe to the carrier. The binder comprises anyelectrically non-conductive material which either decomposes orfluidifies at a temperature within the range in which the fireextinguisher should be discharged for adequate fire protection. Thisrange should be substantially from 175' to 550 F. for differentapplications. Preferably, the binder is a synthetic thermoplastic,typical suitable materials being: cellulose acetate, cellulose acetatebutyrate, acrylics, polyamides, polyethylene, polyurethanes, polyvinylchloride, and polyesters. There also may be used natural rubber orsynthetic rubber. Said synthetic rubbers include Buna S, a copolymer ofbutadiene and styrene; Buna SS, a product with a higher styrene contentthan Buna S; Buna N, a mixed polymer of butadiene and acrylonitrile;polybutene, prepared by the polymerization of isobutane; or Butylrubber, a copolymer of isobutene and butadiene. A limitation in theselection of the binder is that it must not react with the metalparticles to impair the metals electrical qualities.

The carrier 12 is a continuous elongated length of thin flexibleplastic, and is commercially produced by cutting the carrier fromplastic sheet stock. The plastic must be electrically non-conductive toinsulate the stripe 14 from the surface to which the tape is affixed.The plastic is also dimensionally stable and inert to the materialscomprising the stripe 14. The plastic is heat-destructable suitablymodified by the addition of conventional flexibilizing plasticizers, asis well-known to the art.

The adhesive layer 18 is preferably formed from a pressure sensitiveadhesive composition such as plasticized polyisobutylene. The adhesivelayer is protected by a backing (not shown) having a high releasecharacteristic before it is applied to the surface of a structure.Alternatively, the tape 10 can be attached to some surfaces bymechanical fastening means, e.g., stapling or tacking,

taking due care that the stripe 14 is not severed by the fastener.

The stripe material fluidified by a solvent, e.g., naptha or butylacetate is applied to the carrier 12 by any conventional means as forexample by brush painting, spraying, a ruling pen or a striping disc.

invention, Mylar tape such as is used as a carrier for magnetic tape,was utilized as the carrier 12. Mylar is manufactured by the E. I. duPont de Nemours & Co., Inc., Wilmington, Delaware, and is a polyesterfilm which is the condensation product of ethylene glycol and terephthalic acid. This material has been found useful because it isdimensionally-stable and remains flexible to below freezingtemperatures. Its melting point is about 500 F. The Mylar tape used in atested form of my invention has a width of about 0.25" and a thicknessof about 0.0015". In said embodiment a conductive stripe was formed byapplying a line of silver paint. Said paint constituted about 43% finelydivided silver particles, 32.5% of a thermoplastic binder which wasmethyl methacrylate and 24.5% of an organic liquid solvent which wasbutyl acetate. Thus the silver constituent of the dried stripe was about60% by weight of the solids. The line was applied by a ruling pen to theMylar tape carrier and the solvent allowed to evaporate so as to leavethe stripe. The stripe had a cross-section 0.0625" wide and 0.005"thick. A thickness of about one-half to 5 mils constitutes a suitablerange. In said embodiment, the stripe was found to have a resistance of20 ohms/ linear foot.

Turning then to the incorporation of the fire sensing tape 10 into afire detection and extinguishing system, the tape is affixed as by meansof its pressure-sensitive adhesive layer as a continuous length, forexample on the walls and ceiling of a structure, optionally throughseveral continuous rooms, internally or externally of machinery as thehousings of electrical apparatus, or through various compartments ofautomobiles, ships, computors or aircraft. The tape may be installed inany position or orientation, i.e., horizontally, vertically, etc., andwith the tape lying in any desired plane.

As shown in FIG. 1, the stripe 14 forms the major portion of an unbrokenloop and its ends are connected by terminal clips24 to conducting wires26. One of said wires 26 leads to a source of power, e.g., a 6 voltbattery 28 and then to one terminal of a D.C. amplifier, and the otherwire leads to the other terminal of said amplifier. The amplifier outputfeeds and controls a normally closed relay R. The relay in its normallyclosed position energizes a solenoid 30 from an A.C. source of power 31.The solenoid when energized opens a normally closed discharge valve 32which controls the discharge of a fire extinguishing medium from acontainer 34 in which saidmedium is stored under pressure. Thus,breaking the stripe discharges the medium.

The fire extinguishing medium is discharged through a manifold 36, fromwhich lead several discharge ducts 38. The ducts 38 run to differentareas of a structure to be protected, and are perforated as at 40 wheredesired to permit some portion of the extinguishing medium to passthrough the perforations to a local area and to direct the remainder ofthe medium further down the duct.

The actuation of the system takes place at a high speed, far faster thanpreviously known systems.

The sensing tape can readily be utilized with other systems, as forexample where only an alarm is sounded on the breaking of the tape.

A theory may be advanced which, it is believed, accounts for the highfire sensing speed of the described system. First, it will beappreciated that the mass of the stripe and carrier at any one locationis extremely small especially as compared to the mass of theconventional fusible trigger and the trigger holder of existing systems.Consequently, there need be no protracted heat build up over a period oftime, but rather a practically instantaneous reaction to heat or flame.

Second, the carrier 12 itself is heat-destructable, and itself may burnto hasten its own elimination. The removal of the carrier causes thestripe to be without a structural support and thus to fail more suickly.

Third, it must be remembered that the stripe itself does not fuse (dueto the high temperature melting point of the silver particles) butrather the application of heat to the binder causes the binder to melt,writhe, ball-up, curdle, or distort so as to separate the particles andcause a break in the stripe. There is no waiting period for theabsorption of a heat of fusion of the fusible material at a fixedtemperature, before the system will be set off.

Further, it should be appreciated that as the stripe begins to part, theeffective local cross-section of the conductor stripe diminishes. Theconsequent increase in resistivity causes the generation of PR heat,which accelerates the parting of the stripe.-

The following are examples of the effectiveness of my fire sensing tape.The tests were conducted in a room 8' x 8' x 7% high. One wall of theroom contained a door located near one corner thereof, and an adjacentwall of the room near an opposite corner contained a window.

The fire extinguishing agent used was Freon FE 1301 manufactured by E.I. du Pont de Nemours, Wilmington, Delaware. This agent is a liquifiedcompressed bromotrifiourmethane (CB F The extinguishing agent wasdischarged from four discharge ports, each located in a different corneradjacent the ceiling and directed at the center of the room.

TEST 1 Fire.An Underwriters Laboratories Type 1B naptha fire in acanister 0.72 ft. set in the center of the room and two alcohol fires,each 0.72 ft. set in opposite corners of the room.

Tape Lcati0n.Window to ceiling, across ceiling to center of room, backacross ceiling to window.

Time to detect fire.-12 seconds.

Time after detection to extinguish fire.30 seconds.

TEST 2 Fire-Two 0.72 ft. alcohol fires, one on floor, one elevated 2',both 1 from wall opposite door.

Tape l0cati0n.Along wall opposite door, 4' above floor, and then outwindow.

Time to detect fire-34 seconds.

Time after detection to extinguish fire.1l seconds.

Remarks.Tape not parted, conductive stripe balled up and separated. Samefire required 12 minutes to activate 165 F. water sprinkler heads inprevious tests.

TEST 3 Fire.--Type lB naphtha fire, 0.72 ft. in corner, with metal junkpiled in the same corner.

Tape l0czzti0n.Along wall opposite door, above fire and 4 from floor.

Time to detect .fire.5 seconds.

Time after detection to extinguish fire-13 seconds.

Remarks-This is considered a very rapid extinguishment for this type offire, and was primarily due to fast detection time.

TEST 4 F ire.Naphtha soaked paper towels plus a small quantity ofnaphtha in a metal cap were located on the floor in the center of theroom.

Tape l0cati0n.-On a frame 30" above towels.

Time to detect fire.Less than 1 second.

Time after detection to extinguish fire.17 seconds.

Remarks.Detection was practically instantaneous, and the fire wasextinguished so quickly that less than of the paper towels was burned orcharred. Due to quick sensing, the fire did not achieve maximum burningrate.

FIG. 3 illustrates another embodiment of my invention wherein the tapeis in the form of a mat capable of covering a broad area. Therein, thestripe 14' is applied over a carrier 12' which is much wider than thecarrier previously shown. The stripe 14 is laid down in numerous closelyspaced series interconnected parallel rows on the carrier 12 to form anumber of contiguous series connected blocks 42 which constitute theelongated, yet wide, mat 44. The :mat 44 can be cut to fit any desiredarea by severing it between any two blocks 42. The remaining ends of thestripe 14' are then connected to the electricalsystem as heretoforedescribed. The mat embodiment of my invention is utilized in firepronelocations where the nature of the risk demands every precaution be takenby blank-sting the area to be protected with fire sensing tape. Examplesofsuch areas are engine compartments of aircraft and vessels, areas forstoring explosives and fuels, and boiler rooms.

The temperature at which the fire sensing tape is set off can be variedby a judicious selection of the carrier material, the binder material,and the effective cross-section (length and/ or width) of the conductivestripe. The entire length of tape may be of the same temperaturesensitivity, or tapes of various sensitivities can be joined together inseries so that in different locations of the protected structure, thetape will be set off at different critical temperatures. The DCamplifier is employed to enable a very long length of tape to beutilized.

It thus will be seen that I have provided fire sensing tapes and asystem which achieve the several objects of my invention and which arewell adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention,and as various changes might be made in the embodiments set forth, it isto be understood that all matter herein described, or shown in theaccompanying drawings, is to be interpreted as illustrative and not in alimiting sense.

Having thus described my invention, I claim as new and useful and desireto secure by Letters Patent:

1. A temperature sensing tape, for use in a heat detection system,comprising in combination:

(A) an elongated, dimensionally stable, electrically non-conductive,synthetic plastic sheet carrier of slight thickness;

(I) said carrier being composed to be destructible by heat in thetemperature range of from about F. to about 550 F.;

(B) superimposed on said carrier a slender, thin, fiexible stripe ofelectrically conductive-low resistivity metallic material,

(I) said metallic material being composed of finely divided particles ofa low resistance hightemperature-fusing metal dispersed in a solidflexible plastic binder;

(II) said binder being composed to be destructible by heat in the rangeof from about 175 F. to about 550 E;

(III) said stripe being narrower than said carrier, and being adherentto an exposed face of said carrier, and extending continuously along thelength of said carrier,

(C) whereby the indicated degree of heat applied externally to said tapeacts upon said carrier so that it no longer properly supports saidstripe, and acts on said stripe causing it to part so as to interrupt anelectrical circuit.

2. A fire sensing tape as set forth in claim 1 wherein the metal issilver.

3. A fire sensing tape as set forth in claim 1 wherein the binder isthermoplastic.

4. A fire sensing tape as set forth in claim 1 wherein the carrier is apolyester film.

5. A fire sensing tape as set forth in claim 4 wherein the carrier is apolymeric resin constituting the condensation product of ethylene glycoland terephthalic acid.

6. A fire sensing tape as set forth in claim 1 wherein the thickness ofthe stripe is from about one-half to five mils.

7. A fire sensing tape as set forth in claim 1 wherein the stripe isarranged in a pattern providing portions extending transversely acrossthe width of the tape.

8. A fire sensing tape as set forth in claim 1 wherein apressure-sensitive adhesive layer is disposed in the back of thecarrier. 1

ReferencesCited by the Examiner V UNITED STATES PATENTS 1,468,328 9/1923Roe 340-227 2,263,752 11/1941 Babler 200135X Adams et al 340-227 Valente16916 Spears. I

Sun-d1: 200135 Johnston 200135 Boyd 340 227 Davis et a1. 252500 XFOREIGN PATENTS 6/1911 France. 7/1947 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. v

E: W. KIRBY, Examiner.

2,505,761 5/1950 Gieseler 16916 15 H. B. GILSON, Assistant Examiner.

1. A TEMPERATURE SENSING TAPE, FOR USE IN A HEAT DETECTION SYSTEM,COMPRISING IN COMBINATION: (A) AN ELONGATED, DIMENSIONALLY STABLE,ELECTRICALLY NON-CONDUCTIVE, SYNTHETIC PLASTIC SHEET CARRIER OF SLIGHTTHICKNESS; (I) SAID CARRIER BEING COMPOSED TO BE DESTRUCTIBLE BY HEAT INTHE TEMPERATURE RANGE OF FROM ABOUT 175*F. TO ABOUT 550*F.; (B)SUPERIMPOSED ON SAID CARRIER A SLENDER, THIN, FLEXIBLE STRIPE OFELECTRICALLY CONDUCTIVE-LOW RESISTIVITY METALLIC MATERIAL, (I) SAIDMETALLIC MATERIAL BEING COMPOSED OF FINELY DIVIDED PARTICLES OF A LOWRESISTANCE HIGHTEMPERATURE-FUSING METAL DISPERSED IN A SOLID FLEXIBLEPLASTIC BINDER; (II) SAID BINDER BEING COMPOSED TO BE DESTRUCTIBLE BYHEAT IN THE RANGE OF FROM ABOUT 175*F. TO ABOUT 550*F. (III) SAID STRIPBEING NARROWER THAN SAID CARRIER, AND BEING ADHERENT TO AN EXPOSED FACEOF SAID CARRIER, AND EXTENDING CONTINUOUSLY ALONG THE LENGTH OF SAIDCARRIER, (C) WHEREBY THE INDICATED DEGREE OF HEAT APPLIED EXTERNALLY TOSAID TAPE ACTS UPON SAID CARRIER SO THAT IT NO LONGER PROPERLY SUPPORTSSAID STRIP, AND ACTS ON SAID STRIPE CAUSING IT TO PART SO AS TOINTERRUPT AN ELECTRICAL CIRCUIT.